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SubjectRe: [tcp] e926147618: stress-ng.icmp-flood.ops_per_sec -8.7% regression

On Wed, Jun 08, 2022 at 09:34:41AM +0200, Willy Tarreau wrote:
> On Wed, Jun 08, 2022 at 10:26:12AM +0300, Moshe Kol wrote:
> > Hmm, How is the ICMP flood stress test related to TCP connections?
> To me it's not directly related, unless the test pre-establishes many
> connections, or is affected in a way or another by a larger memory
> allocation of this part.

Fengwei and I discussed and thought this could be a data alignment
related case, that one module's data alignment change affects other
modules' alignment, and we had a patch for detecting similar cases [1]

After some debugging, this could be related with the bss section
alignment changes, that if we forced all module's bss section to be
4KB aligned, then the stress-ng icmp-flood case will have almost no
performance difference for the 2 commits:

10025135 +0.8% 10105711 ± 2% stress-ng.icmp-flood.ops_per_sec

The debug patch is:

diff --git a/arch/x86/kernel/ b/arch/x86/kernel/
index 7fda7f27e7620..7eb626b98620c 100644
--- a/arch/x86/kernel/
+++ b/arch/x86/kernel/
@@ -378,7 +378,9 @@ SECTIONS

/* BSS */
- .bss : AT(ADDR(.bss) - LOAD_OFFSET) {
+ .bss : AT(ADDR(.bss) - LOAD_OFFSET)
+ {
__bss_start = .;
The 'table_perturb[]' used to be in bss section, and with the commit
of moving it to runtime allocation, other data structures following it
in the .bss section will get affected accordingly.


> Willy

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